This invention relates to flame retardants of the antimony oxide type. It particularly involves improved colloidal antimony pentoxides for use in polyvinyl chloride polymers or for use with aliphatic bromine compounds added to various polymers.
For many years, antimony oxide has been used in conjunction with organic chlorides, bromides and other halogen-containing materials as a coating for fabrics, textiles, plastics and the like for rendering the same flame retarding. Such compounds are described, for example, in "The Chemistry and Uses of Fire Retardants," by J. W. Lyons (Wiley--Interscience: New York, 1970), pp. 17, 18, 21 and 79. While the reasons for the resulting flame-retardant properties are not fully understood, one school of thought is that an antimony oxide halogen compound may be generated in situ, which interrupts oxidizing reactions and thus inhibits the flame. In any event, the prior art has principally involved antimony oxide in the form of Sb.sub.2 O.sub.3 and in pigmentary particle size, generally of the order of 1/2 to 1 micron.
While these prior antimony oxide compounds have been widely used, they are subject to rather serious deficiencies and drawbacks which have just had to be tolerated. It has been found that the pigmenting characteristics of thse pigment-size particles often impair the color of the dyed fabric; or, when cast, as in films, plastics and resins, producing a milky, rather than a clear cast.
U.S. Pat. Nos. 3,860,523 and Re. 31,214 teach that antimony pentoxide in colloidal sol form remarkably overcomes every one of the above-described difficulties and, in addition, does so with greater efficiency, enabling the quantity of antimony required for a predetermined degree of flame-retarding to be substantially reduced below that required by pigment-grade particles. The colloidal particles of antimony oxide can be used as colloidal dispersions in water or dried to provide powders. Either of these forms can be readily formulated into various polymer systems combined with a source of halogen to provide effective fire retardancy. The lower refractive index of 1.7 together with the small size of the colloid (20 to 1000 angstroms) compared with the large size of the powder (10-40 microns) result in low pigmenting characteristics.
U.S. Pat. Nos. 3,860,523 and Re. 31214 (3,960,989) disclose that colloidal Sb.sub.2 O.sub.5 can be prepared by dissolving potassium antimonate with some excess of KOH to form a solution that contains about 2% by weight of Sb.sub.2 O.sub.3. This solution is passed through a cation exchange resin in the hydrogen form to yield insoluble Sb.sub.2 O.sub.5 which may also be called antimonic acid. The particles of Sb.sub.2 O.sub.5 being of colloidal size remain dispersed. As the concentration of Sb.sub.2 O.sub.5 is increased, some particle growth and agglomeration takes place but the colloidal dispersion is still stable. The pH of this material is low, about 1.5, but can be varied without adversely affecting the colloid.
U.S. Pat. No. 4,110,247 teaches that a colloidal dispersion of Sb.sub.2 O.sub.5 can be made from sodium antimonate. A slurry of the very slightly soluble sodium antimonate is circulated through a bed of cation exchange resin. As the small proportion of sodium ion solution is exchanged for hydrogen, more of the antimonate can go into solution. Finally most of the antimonate has been solubilized and the sodium exchanged, forming a colloidal dispersion of the antimony pentoxide. At this point the pH is about 1.7 and the product is similar to that described in the previously discussed patents.
U.S. Pat. No. 4,307,148 teaches that fibrous materials that contain cotton or are cotton substitutes can be treated with an alkali metal polyantimonate solution of a pH of about 8 absent any halogen to provide fire retardant properties. The alkali metal can be sodium or potassium.
None of these patents address an essential problem that has prevented the use of colloidal antimony pentoxide as a fire retardant in some formulated polymers. The colloidal Sb.sub.2 O.sub.5, when dried from the colloidal dispersions, forms a powder wherein the particles are of colloidal dimensions. When these powders are included in polymers that are thermoplastic, thermoset or otherwise exposed to heat, the polymer is degraded. It is an object of this invention to provide colloidal Sb.sub.2 O.sub.5 powders that can be formulated into polymers without degradation on exposure to heat.